1. Field of the Invention
The present invention relates to a method of manufacturing a single crystal of silicon through use of the Czochralski method (CZ method) in which a single crystal of silicon is manufactured using a quartz crucible after a magnetic field is applied to the crucible so as to restore the inner surface of the crucible or to prevent the inner surface of the crucible from deteriorating.
2. Description of the Related Art
When a single crystal of silicon is pulled from silicon melt within a quartz crucible in accordance with the CZ method, the inner surface of the crucible is exposed to the silicon melt, which has a high temperature. As a result, the condition of the inner surface of the crucible changes and deteriorates; i.e., so-called cristobalite, a substance that hardly melts into the silicon melt, separates from the inner surface of the crucible. When such a refractory substance separates from the inner surface of the crucible and adheres to the surface of a single crystal of silicon being pulled, a dislocation is generated in the single crystal.
Especially, in manufacture of a single crystal of silicon having a diameter equal to or greater than 8 inches needed so as to cope with the recent increases in the degree of integration and the degree of accuracy of semiconductor devices, the inner surface of a quartz crucible deteriorates easily, and therefore the problem of dislocation generation is apt to occur. That is, in order to manufacture a single crystal of silicon having a diameter equal to or greater than 8 inches, a quartz crucible having a large diameter equal to or greater than 600 mm must be used. In order to melt a large amount of silicon material within such a large-diameter quartz crucible and to maintain the thus-obtained silicon melt, a high-power graphite heater must be used as a heating element. As a result, the quartz crucible itself is heated to a higher temperature. The higher the temperature to which the quartz crucible is heated, the higher the possibility of occurrence of deterioration of the inner surface, that is in contact with high-temperature silicon melt. Further, in order to pull a single crystal of silicon from a quartz crucible, the temperature of the silicon melt at a position where the crystal is growing (i.e., at the central portion) must be maintained at a temperature that allows the silicon melt to solidify. Therefore, when the quartz crucible has a large diameter as described above, the graphite heater for the crucible must have a large power rating, because the center portion is separated from the graphite heater more than is that in a quartz crucible having a smaller diameter. Consequently, the quartz crucible having a larger diameter is heated to a higher temperature, so its inner surface exposed to silicon melt deteriorates more easily.
The above-mentioned deterioration of the inner surface of a quartz crucible also occurs in the multi-pulling method (see Semiconductor Silicon Crystal Technology, Fumio Shimura, pp. 178-179, 1989) wherein a silicon material is recharged so as to manufacture a plurality of single crystals of silicon from the same crucible; as well as in the Continuous Czochralski (CCZ) method in which a single crystal of silicon is manufactured while a silicon material is being supplied to a crucible. In these methods, the operation hours of the quartz crucible becomes longer, so that the inner surface of the quartz crucible deteriorates, resulting in generation of dislocations in single crystal of silicon. Therefore, in the multi-pulling method, production of a single crystal of silicon becomes impossible to continue, and in the CCZ method, production of a single crystal of silicon must be stopped halfway.
Accordingly, there has been demanded a method of manufacturing a single crystal of silicon that can reduce the possibility of causing deterioration of the inner surface of a quartz crucible or can restore the deteriorated inner surface of the crucible, thereby making it possible to manufacture a single crystal of silicon having a large diameter while preventing generation of dislocation. Further, in relation to the multi-pulling method, it has been demanded to manufacture a larger number of single crystals of silicon from a single quartz crucible, and in relation to the CCZ method, it has been demanded to operate over a longer period of time using a single quartz crucible, thereby making it possible to manufacture a longer single crystal.